This invention relates to electrophotography, and more particularly, to an improved overcoated electrophotographic imaging member and method of making the electrophotographic imaging member.
Generally, electrophotographic imaging processes involve the formation and development of electrostatic latent images on the imaging surface of a photoconductive member. The photoconductive member is usually imaged by uniformly electrostatically charging the imaging surface in the dark, and exposing the member to a pattern of activating electromagnetic radiation, such as light, which selectively dissipates the charge in the illuminated areas of the member to form an electrostatic latent image on the imaging surface. The electrostatic latent image is then developed with a developer composition containing toner particles which are attracted to the photoconductive member in image configuration. The resulting toner image may be transferred to a suitable receiving member such as paper.
The imaging surface of many photoconductive members is sensitive to wear, ambient fumes, scratches and deposits which adversely affect the electrophotographic properties of the imaging member. Overcoating layers have been proposed to overcome the disadvantageous characteristics of these photoreceptors. However, many of the overcoating layers adversely affect electrophotographic performance of the electrophotographic imaging member.
One type of insulating electrophotographic imaging member has at least one photoconductive layer and an overcoating layer comprising an insulating, film forming continuous phase comprising charge transport molecules and finely divided charge injection enabling particles dispersed in the continuous phase.
Overcoatings for photoreceptors have been disclosed in U.S. Pat. No. 4,515,882. These overcoatings comprise an insulating film forming continuous phase comprising charge transport molecules and finely divided charge injection enabling particles dispersed in the continuous phase. The imaging members have at least one photoconductive layer and the overcoating layer. Where desired, a barrier layer may be provided in the device interposed between the photoconductive layer and the overcoating layer. The devices disclosed in U.S. Pat. No. 4,515,882 can be employed in an electrophotographic imaging process in which the outer imaging surface of the overcoating layer is uniformly charged in the dark. A sufficient electric field is applied across the electrophotographic imaging member to polarize the charge injection enabling particles whereby the charge injection enabling particles inject charge carriers into the continuous phase of the overcoating layer. The charge carriers are transported to and trapped at the interface between the photoconductive layer and the overcoating layer, and opposite space charge in the overcoating layer is relaxed by charge emission from the charge injection enabling particles to the imaging surface. The overcoating layer is essentially electrically insulating prior to deposition of the uniform electrostatic charge on the imaging surface.
The mechanism by which charge passes through the overcoating to the photoreceptive surface in known devices is believed to involve the electric field, formed by corona charging of the electrophotographic device, instantly polarizing the charge injection enabling particles or species. Charge, for example, in the form of holes, is injected into the hole transport phase of the overcoating and is driven by the charging field to the interface between the overcoating and photoconductive layer. The charge is stopped at the interface by a blocking layer or because there is no injection into the photoreceptor. The negative space charge in the bulk of the overcoating is relaxed by a charge emission.
However, overcoatings such as those disclosed in U.S. Pat. No. 4,515,882 suffer from the disadvantage of high light absorption and scattering in the coating due to pigment loading and particle size. Inorganic charge injection enabling particles mentioned in that patent include carbon black, molybdenum disulfide, silicon, tin oxide, antimony oxide, chromium dioxide, zinc dioxide, titanium oxide, magnesium oxide, manganese dioxide, aluminum oxides, colloidal silica, graphite, tin, aluminum, nickel, steel, silver, gold, other metals and their oxides, sulfides, halides and other salt forms, etc. Such charge injection enabling particles tend to reduce the photosensitivity of the photoreceptor. For example, one weight percent of carbon black pigment, which is the prime effective charge injection enabling species currently in use, reduces light transmission to the photosensitive layer by about 20%.
Electrophotographic devices have been proposed which include layers that are electrically conducting and transparent. For example, U.S. Pat. No. 3,505,131 discloses a method of preparing a highly transparent cuprous iodide conductive film. U.S. Pat. No. 3,677,816 discloses a method of producing transparent and electrically conducting coatings of copper iodide. These films are used as an electrode or ground in multielectrode electrostatic systems.
Copper iodide has also been used in electrophotography in protective layers, as disclosed in Japanese Unexamined Patent Application No. 59-159 (1984). The disclosed protective layer comprises 10-60 weight percent Cu iodide based on binder resin.
Another use of copper iodide in electrophotography is disclosed in U.S. Pat. No. 4,133,933. Cuprous iodide is provided in an electrosensitive recording sheet, and is whitened by adding an alkaline substance for increasing the resistance of the cuprous iodide and for increasing the contrast of the recorded mask.
In the above-described devices, copper iodide is utilized primarily to achieve high electrical conductivity.
There continues to be a need for improved layers in electrophotographic imaging members which are highly transparent and which will protect the imaging member from wear, ambient fumes and the like.